1. Field of the Invention
The present invention relates to a sheet stacking apparatus on which a sheet is stacked and to an image forming apparatus including the same.
2. Description of the Related Art
In general, an image forming apparatus such as a printer is provided with a sheet feed cassette storing a sheet at a lower part of a main body such that the sheet feed cassette can be drawn out of/inserted into the main body. In connection with such image forming apparatus, Japanese Patent Application Laid-open No. 2007-145551 for example proposes an image forming apparatus in which a bottom surface of a sheet storage cassette composes a bottom surface of a main body and the sheet storage cassette is provided with a projection such as a rib at the bottom surface thereof in order to reduce an interference between the sheet storage cassette and an installation surface where the image forming apparatus is installed.
Still further, there is known an image forming apparatus provided with a plurality of stages of sheet feed cassettes in order to store various types of sheets and a large volume of sheets.
Lately, it is required to downsize the image forming apparatus in a height direction from aspects of operability and storability. Still further, the image forming apparatus including a plurality of stages of sheet feed cassettes is required to improve designability and to cut cost by cutting a number of parts by providing no intermediate cover between these plurality of sheet feed cassettes and by reducing gaps between the sheet feed cassettes.
However, the following problems occur if the sheet feed cassettes are provided in close proximity with each other. FIGS. 14A and 14B illustrate one example of such case. As shown in FIG. 14A, the image forming apparatus 300 includes sheet feed cassettes 301 and 302 provided at two stages of upper and lower stages. In terms of an exterior of the sheet feed cassettes, a boundary between the upper and lower sheet feed cassettes is formed by an exterior cover 311 composing the sheet feed cassette 301 and an exterior cover 312 composing the sheet feed cassette 302. In a state in which the sheet feed cassettes 301 and 302 are stored in the image forming apparatus 300, a gap between the exterior covers 311 and 312 is a distance H.
Suppose here that the upper sheet storage cassette 301 fully loaded with sheets is drawn out in a state in which the lower sheet storage cassette 302 is being precedingly drawn out as shown in FIG. 14B for example. The sheet feed cassette 301 hangs downward because a cassette base and a cassette rail deform due to weight of the sheets SS and the sheet feed cassette 301. In a case when a vertical distance of the sheet feed cassette 301 hanging downward exceeds the distance H between the exterior covers 311 and 312, there is a case when a lower corner edge 311a of the exterior cover 311 interferes with an upper corner edge 312a of the exterior cover 312, thus disabling the sheet feed cassette 301 to be fully opened. Thereby, there is a case when an enough space necessary for replenishing sheets SS into the sheet feed cassette 301 cannot be assured or the lower sheet storage cassette 302 cannot be closed. Noted that it is unable to prevent the upper sheet storage cassette 301 from interfering with the lower sheet storage cassette 302 even if a projection is provided on a lower surface of the lower sheet storage cassette 302 like a sheet storage cassette disclosed in Japanese Patent Application Laid-open No. 2007-145551.